Schedule backup at regular interval

[pm47]

This is a bit less trigger happy than previously, and the implementation
is simpler.

[codecov-commenter]

Codecov Report

Merging #1845 (83ed672) into master (afb1b41) will decrease coverage by 0.15%.
The diff coverage is 74.35%.

@@            Coverage Diff             @@
##           master    #1845      +/-   ##
==========================================
- Coverage   89.09%   88.93%   -0.16%     
==========================================
  Files         146      150       +4     
  Lines       10994    11237     +243     
  Branches      444      429      -15     
==========================================
+ Hits         9795     9994     +199     
- Misses       1199     1243      +44     

Impacted Files	Coverage Δ
...ir-core/src/main/scala/fr/acinq/eclair/Setup.scala	79.88% <14.28%> (-0.48%)	⬇️
...n/scala/fr/acinq/eclair/db/FileBackupHandler.scala	86.20% <86.20%> (+14.77%)	⬆️
...re/src/main/scala/fr/acinq/eclair/NodeParams.scala	92.85% <100.00%> (+0.11%)	⬆️
...clair/blockchain/bitcoind/rpc/BatchingClient.scala	86.36% <0.00%> (-13.64%)	⬇️
...lockchain/bitcoind/rpc/ExtendedBitcoinClient.scala	93.93% <0.00%> (-2.49%)	⬇️
.../acinq/eclair/blockchain/bitcoind/ZmqWatcher.scala	96.09% <0.00%> (-0.79%)	⬇️
...eclair/blockchain/bitcoind/BitcoinCoreWallet.scala	89.70% <0.00%> (-0.71%)	⬇️
...c/main/scala/fr/acinq/eclair/channel/Channel.scala	86.19% <0.00%> (ø)
...n/scala/fr/acinq/eclair/channel/ChannelTypes.scala	97.14% <0.00%> (ø)
...la/fr/acinq/eclair/transactions/Transactions.scala	96.78% <0.00%> (ø)
... and 9 more